Most refrigeration compressors use mineral oil lubricants with chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) refrigerants. In addition to being inexpensive and rugged lubricants, mineral oils are miscible with
CFCs and HCFCs, which is important in providing good oil return. In a system with poor oil return, the oil that leaves the compressor collects at various points in the refrigeration system and does not return to the compressor, leading to clogging, poor lubrication, and decreased efficiency.
With the continued regulatory pressure limiting the use of ozone depleting substances, the refrigeration industry has been moving to non-ozone depleteing hydrofluorocarbon (HFC) based refrigerants. HFCs, however, lack the miscibility with traditional lubricants such as mineral oils necessary to provide adequate performance. This has resulted in the implementation of oxygenated lubricants such as polyol ester (POE) oil, polyalkylene glycol (PAG) oil, and polyvinyl ether (PVE) oil. These new lubricants can be considerably more expensive than traditional mineral oil lubricants and can be extremely hygroscopic. Their combination with water can result in the undesirable formation of acids that can corrode parts of the refrigeration system and lead to the foramtion of sludges. Consequently, there is a need and opportunity to resolve this low solubility and oil return problem so that the refrigeration industry may utilize HFC-based refrigerants with mineral oil and/or oxygenated lubricants.
The present invention addresses these needs of the refrigeration industry by providing polymeric oil-return agents which create a solution or stabilized dispersion of lubricant oil (dispersed phase) in a HFC, HFO, and/or HCFC-based refrigerant (continuous phase), permitting improved lubricant oil transport through a refrigeration system and lubricant oil return back to the refrigeration system compressor from other refrigeration system zones. The polymeric oil-return agents of the present invention are effective when used in combinations with conventional mineral oils and/or oxygenated oils.
U.S. Pat. No. 6,516,837 discloses the use of surfactants and solubilizing agents with environmentaly desirable refrigerants in systems where chlorine containnig refrigerants are being replaced with non-chlorine containng refrigerants. The patent discloses that the surfactants/solubilizing agents are needed because many non-chlorine-containing refrigerants, including HFC's, are relatively insoluble and/or immiscible in the types of lubricants traditionally used such as mineral oil and alkylbenzenes or polyolefins. The patent discloses that the surfactants may include polymers, preferably of polyoxyethylene-type nonionic surfactants, or copolymers of methacrylates with N-substituted compounds; copolymers which incorporate polyester linkages, and the like.
U.S. Pat. No. 6,299,792 discloses the use of combinations of surfactants and solubilizing agents additives as oil return agents for refrigeration systems.